What is XML?
XML, the eXtensible Markup Language, is the new markup language and it
is subset of and is based on mature markup language called Standard
Generalization Markup Language (SGML). XML looks very similar to
HTML version but
unlike HTML, XML is not actually a language on its own right but it is a
meta-language. It is used to develop other languages by allowing the use
of custom tags like (<flat>, <rooms>, <price>). The great example of
developing other languages from XML is XHTML, though XML is not direct
replacement of HTML but future version of HTML will be based on XML
called XHTML.
The flexible representation of data allows users to send, receive and
transform the data very easily. The use of XML is rapidly growing
because of the great use of XML in data transfer with and without
internet for example Businesses can use XML to send the pricing data of
products. The growing use of XML is also seen in different tools, web
technologies and techniques for example AJAX which uses XML-
HTTP-REQUEST.
XML is also used for long term data storage.
XML is all about data representation and it does not provide any thing
for presentation however other technologies like CSS and XSLT can be
used for the presentation of XML data.
All the XML documents are passed through the XML specification complied
parser called XML parser to ensure the correctness of data in it. The
parser ensures that the XML document is well-formed by checking its
structure and syntax and it may also be used to check the validity of
the user's data structure. The XML parsers use external document called
schema to validate the XML document. There are two commonly used schemas
to validate XML data or documents. One of them is DTD which is used for
basic validation for example it can not validate the type of data and
other type is schema is XML schema which is advanced and have many
features as compared to DTD.